Hello friends..i have some question regarding lm3886 chipamp, i hope you will help me.
1)Any increase in output dc offset if i use 47k as input impedance(with 1uf input cap) & 22k as feedback resistor?
i heard that it is recommended to use same value input(to ground) & feedback resistor for minimal dc offset.
i have 22k potentiometer only, this is why i am thinking about to use 47k input impedance.
(Ci would be 47uf with 680ohm fb shunt).
2) i am going to use 22-0-22vAC 5amp trafo for lm3886tf package(4ohm-stereo), any advice regarding thermal consideration & supply capacitance?
3) Is it always recommended to use zobel (2.7ohm & 0.1uf cap) with thiele network; specially for 4ohm load?
your help would be appreciated
1)Any increase in output dc offset if i use 47k as input impedance(with 1uf input cap) & 22k as feedback resistor?
i heard that it is recommended to use same value input(to ground) & feedback resistor for minimal dc offset.
i have 22k potentiometer only, this is why i am thinking about to use 47k input impedance.
(Ci would be 47uf with 680ohm fb shunt).
2) i am going to use 22-0-22vAC 5amp trafo for lm3886tf package(4ohm-stereo), any advice regarding thermal consideration & supply capacitance?
3) Is it always recommended to use zobel (2.7ohm & 0.1uf cap) with thiele network; specially for 4ohm load?
your help would be appreciated
hello.........there are some threads that can answer your questions.........you can use the search button -
or look here to begin:
https://www.diyaudio.com/forums/chip-amps/330705-learning-lm3886-amps.html#post5619685
or look here to begin:
https://www.diyaudio.com/forums/chip-amps/330705-learning-lm3886-amps.html#post5619685
You'll probably find this informative: http://www.ti.com/lit/an/sloa059/sloa059.pdf
Especially pages 15-17.
Tom
Especially pages 15-17.
Tom
Very informative tom! Maybe i should start from basics
Actually i know electronics but not much! Ok..but my questions still unanswered i don't have 10-25k pot... 22-47k only. What should be Amps input resistor (Zin) then? & what about supply capacitance? Is 10000uf(per rail) sufficient for stereo? if i am not wrong, this chip can produce 11amp of current at peak. plz help me with some math. Regards.
Build amplifier just as recommended in the datasheet.
You can use a larger or smaller value volume pot, no big deal ... and at maximum volume it is out of the signal path anyway.
All you´ll notice is that at half way it´s *a little* less loud than expected ... IF you notice it at all.
You are going to cook your poor LM3886
a) too high transformer voltage ... you should use 18+18VAC .
b) plus 4 ohm impedance.
c) plus you use the worst dissipation package, the plastic encapsulated TF version.
Which was designed to save assembly time in mass produced TVs, Home Theater and similar "light duty" applications, but you probably wantb to pull out maximum possible power, so: metallic case, good heatsinking and mica + thermal paste.
Always use a Zobel network, doubly so on a chipamp .
Also decouple chip with a close mounted 0.1uF ceramic cap as suggested in datasheet.
I have no option... it's hard to find T package here & i have lm3886tf only(total of eight piece , pretty expensive you know) 
But what are you saying?! According to datasheet* it can handle +/-30vDC with 4ohm load but with bigger heatsink! [No prohibition for using TF package at +/-30vDC] Don't you think so? I know you Mastered in electronics..but just sayin
Any advantage using bigger value than 0.1uf cap at chip supply pins....220nf-1uf??
, pretty expensive you know) But what are you saying?! According to datasheet* it can handle +/-30vDC with 4ohm load but with bigger heatsink! [No prohibition for using TF package at +/-30vDC] Don't you think so? I know you Mastered in electronics..but just sayin Any advantage using bigger value than 0.1uf cap at chip supply pins....220nf-1uf??
You are going to cook your poor LM3886
a) too high transformer voltage ... you should use 18+18VAC .
Um. No. 2x22 VAC is about right. You'll get ±30 V, which is perfect for the LM3886 at 4 Ω load. The ABS MAX is ±42 V with signal applied, so you have plenty of margin there. At ±30 V you'll reach 40 W dissipation in the LM3886, which the isolated TF package can easily handle if mounted on a proper heat sink (1.4 K/W per LM3886). See math here: LM3886 chip power amplifier thermal design.
Agree on the Zobel (and Thiele) networks. +1 on decoupling, though you need the full 470 uF + 10 uF + 0.1 uF recommended in the data sheet. Or use more modern parts as I do: LM3886 chip amp supply decoupling.
Tom
Could you post the link from TNT Please, thanks
Yes, why not?
Solid State Power Amplifier Supply Part 3
Hi...i need some advice before buying some components & assembling the circuit, please guide me. Actually i have made lm3886 gc, but this time i want to make it better.
1)For thiele network NS recommends 0.7uh inductor with 10ohm resistor, but your recommendation is 1.5ohm resistor with 2uh coil to better dampen the ringing under capacitive load. i would like to follow your suggestion, but what would be the power rating of that 1.5ohm resistor? 2watt?
2)For zobel datasheet recommends 2.7ohm resistor with 0.1uf cap. But some forum member disagree with that, they say 2.7ohm is a very light load for lm3886. What should i choose...4.7ohm/10ohm resistor or i should follow national guidelines?
3) is it nessesary to use Cc, Cf, Rf2 ?
4)For mute my calculation is based on your method,
P.supply is +/-30vDC
((2/3)×30-3)/0.0005 =34,000
i'll choose 33kohm with 100uf cap.
One more thing, now i have no confusion over dc offset & potentiometer choice, thanks to you. Sorry for my poor English
Regards.
Keep feedback resistor path as short as possible.
1mm pcb track = 1nH so the inductance and phase shift can soon mount up.
Probably my final & last chipamp build!
Hi tomchr....i am ready to start my work but i am unable to find 1.5ohm resistor as you suggested in another thread for better transient response(2uh inductor coil in parallel). i have 1ohm/2.2ohm resistors. please suggest what would be better & i am going to use all optional components including Cc,Cf2,Rf2. Soon i'll post photos.
Hi tomchr....i am ready to start my work but i am unable to find 1.5ohm resistor as you suggested in another thread for better transient response(2uh inductor coil in parallel). i have 1ohm/2.2ohm resistors. please suggest what would be better & i am going to use all optional components including Cc,Cf2,Rf2. Soon i'll post photos.
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